1. Field of the Invention
The present invention relates to a deflection yoke, which is used with an in-line type cathode ray tube (CRT), and particularly relates to a deflection yoke for adjusting a characteristic of a magnetic field, such as convergence or purity, by rotating a multipolar magnetic ring mounted on a cylindrical neck portion of such deflection yoke.
2. Description of the Related Art
Generally, a deflection yoke, which is used with an in-line type CRT (cathode ray tube), has a multipolar, for example, dipole or quadrupole magnetic ring. The multipolar magnetic ring is used for adjustment of a magnetic field characteristic such as the convergence or the purity of CRT by tuning a position of such multipolar magnetic ring.
FIG. 11 is a perspective view for explaining an example of a deflection yoke for a CRT. In FIG. 11, the deflection yoke for a CRT comprises a pair of separators 1a and 1b made by an insulating material on the narrower diameter portion of the deflection yoke, a pair of horizontal deflection coils (not shown) in inside of the deflection yoke, and a pair of vertical deflection coils 7 on the outside and the wider diameter portion of the deflection yoke, and a pair of cores 2 on the outer side of the vertical deflection coil 7, a flange 1f is formed in a narrower diameter side of the first separator 1a and the second separator 1b, and a cylindrical neck portion 103 is formed in the flange 1f. 
FIG. 12 is a partial perspective view for explaining the example of the deflection yoke shown in FIG. 11 for a CRT. In FIG. 12, the cylindrical neck portion 103 having tongues 3a through 3f, is formed on a flange 1f with the first and second separators 1aand 1b. 
The cylindrical neck portion 103 is inwardly flexible as it has slits 4a through 4f. A clamp band 5 for fixing the deflection yoke to a neck of the CRT is provided on the neck portion 103. A screw 6 is screwed to the clamp band 5, and fastens the deflection yoke to the neck of the CRT by tightening the clamp band 5 about the neck portion 103.
Each magnetic ring 10 and 11 has multipolar magnet and is provided between the clamp band 5 and the flange 1f of the first and second separators 1a and 1b. FIG. 12 shows the clamp band 5 and the magnetic rings 10 and 11 being removed from the neck portion 103. Generally, the magnetic rings 10 and 11 comprise of material dispersed with magnetic powder such as Barium ferrite or Alnico alloy substance evenly on a nylon plastic. The inner diameter of the magnetic rings 10 and 11 is nearly equal to the outer diameter of the neck portion 103.
More precisely, protrusions 12a and 12b are flexible in the direction of the Z axis or the longitudinal direction of the neck of the CRT, and are provided at the bottom of the neck portion 103. A hook 13 having a claw 13a of triangular shape at their distal ends are formed on the tongues 3c and 3f of the neck portion 103. The magnetic rings 10 and 11 are inserted from the rear side of the deflection yoke, about the neck portion 103 having a cylindrical shape, between the protrusions 12a and 12b, and the claw 13a. 
A prominence 14 is formed on the upper area of the tongues 3c and 3f for engaging with holes 5a and 5b of the clamp band 5 respectively. The prominence 14 is sloped away from the neck portion 103 and toward the bottom thereof. As. the hook 13, is flexible, the magnetic rings 10 and 11 are easily set to a predetermined position of the neck portion 103. The distance between the protrusions 12a and 12b, and the claw 13a is shorter than the thickness of the magnetic rings 10 and 11 put together, so that a bounce force of the protrusions 12a and 12b is applied on the magnetic rings 10 and 11 when such rings are inserted between the protrusions 10 and 11, and the claw 13a. 
A deflection yoke is attached to a CRT to control magnetic filed characteristic such as convergence, and such control is performed by rotating the position of magnetic rings 10 and 11. An adequate (rotational) torque is added for tuning position of the magnetic rings 10 and 11 by the protrusions 12a and 12b, and the claw 13a, so that the magnetic rings 10 and 11 may not loosely rotate after the tuning and until a glue fixes the appropriate position of the magnetic rings 10 and 11. The rotating torque is obtained by a frictional force occurred by a bounce force of the protrusions 12a and 12b in upward direction of Z axis in FIG. 12.
According to the above prior art mentioned, a width of a slit between the tongues 3a through 3f and the pair of magnetic rings 10 and 11 becomes bigger as the neck portion 103 becomes narrower by tighten a bolt 6 to make inner circle of the clamp band 5 smaller. A neck portion of the CRT has a variation of the thickness, and the width of a slit between the tongues 3a through 3f and the pair of magnetic rings 10 and 11 becomes more bigger when the deflection yoke is attached to the neck portion, which has thinner circle. As a result, a pair of tongues 13 holds the pair of the magnetic rings 10 and 11 from the inner circumference of the magnetic ring in the radial direction.
However, the tongues 13 is flexible inwardly to the neck portion 103 as a inward force pushes one of the tongues 13 at the tuning of the magnetic rings 10 and 11 that the magnetic rings 10 and 11 are released from the tongue 13. Then the magnetic rings 10 and 11 are disengaged from the attached position between the protrusions 12a and 12b, and the claw 13a. 
Accordingly, in consideration of the above-mentioned problem of the related art, an object of the present invention is to provide a deflection yoke of which a magnetic ring is attached to the neck portion, to control convergence by tuning such magnetic ring, and which can prevent a magnetic ring from being disengaged from a neck portion without losing smooth attachment to the neck portion.
In order to achieve the above object, the present invention provides, according to an aspect thereof, a deflection yoke for a cathode ray tube comprising: separator means in a funnel shape having a narrower diameter portion and a wider diameter portion, wherein a neck portion in a cylindrical shape is formed on said narrower diameter portion; magnetic ring means rotatably mounted on said neck portion; holding means having at least a pair of holding portions for holding said magnetic ring means from said narrower diameter portion side and said wider diameter portion side respectively, wherein said holding portion of narrower diameter portion side has an inwardly flexible portion; and inflexible holding means having a substantially inflexible portion for restricting position of said magnetic ring means where said inflexible holding means substantially contacts the inner circumference surface of said magnetic ring means after said magnetic ring means is attached to thereto.
Other objects and further features of the present invention provides the deflection yoke as mentioned above, wherein said inflexible holding means is combined with said flexible holding means, and wherein said flexible holding means and said inflexible holding means are formed in distant position on circular direction of said neck portion.
Other object and further features of the present invention provides the deflection yoke as mentioned above, wherein said inflexible holding means is formed separately with said flexible holding means, and wherein said flexible holding means and said inflexible holding means are formed in distant position on circular direction of said neck portion.
Other object and further features of the present invention provides the deflection yoke as mentioned above, wherein said inflexible holding means is formed separately with said flexible holding means, and wherein said flexible holding means and said inflexible holding means are formed in identical position of circular direction of said neck portion.
A deflection yoke incorporating the principles of the present invention will be. described in detail with reference to the accompanying drawings, in which the same reference numerals and symbols are used to denote like or equivalent elements used in the aforementioned prior art deflection yoke, and the detailed explanation of such elements are omitted for simplicity.